Electric cells with self-supporting porous ceramic plate

ABSTRACT

An electric cell 10 comprising a ceramic porous plate 12 which has previously been soaked in sulphuric acid such that a substantial volume of the pores contain sulphuric acid. Spaces are provided on either side of the plate 12 by a casing 14. The spaces are respectively filled, one with powdered lead-oxide 16, and the other with lead powder 18. Strips of lead 20, 22 extend from adjacent the base of the casing 14 through respectively the lead oxide 16 and the lead powder 18 and through an upper removable cap 24 of the casing 14 to provide terminals 26, 28.

This application is a PCT application.

This invention concerns improvements in or relating to electric cellsand particularly but not exclusively lead-acid accumulators.

Lead-acid accumulators are commonly used, and particularly in motorvehicles, to take advantage of the high current which can be obtainedfrom them. However, a number of disadvantages are experienced with suchaccumulators. These accumulators contain liquid sulphuric acid and thushazardous spillage may occur, particularly in the occurrence of anaccident such as the accumulator being dropped or a road accident. Forthis reason in certain situations such as on board ships, lead-acidaccumulators are often not permitted. Further such accumulators arerelatively bulky and particularly heavy thus making transportationdifficult. This is of particular relevance in for instance mines whereminers may carry such accumulators to power their head lamps.Furthermore if a lead accumulator is overcharged, gaseous hydrogen andoxygen may be given off and thus a system of venting is required whichfurther increases the likelihood of acid spillage. The relative weightof such accumulators reduces their effective use in electrically poweredvehicles.

According to the present invention there is provided an electric cellcomprising a self supporting porous member in which a liquid electrolyteis absorbed, and means for locating a first material in contact with themember to constitute the anode and a second material in contact with themember to constitute the cathode.

The porous member is preferably substantially rigid.

Preferably the first and second materials are respectively in contactwith opposite sides of the member.

Electrical conductors preferably extend through the cell in contactrespectively with either the first or second materials. The conductorsmay be provided on the porous member and may be printed thereon and maycomprise printed gold.

Additional electrical conductors preferably extend from the conductorsin contact with the first and second materials, externally of the cellto provide terminals for the cell.

The porous member is preferably made of a ceramic material.

The porous member desirably has a substantially planar configuration andthe exterior of the porous member may be contoured.

The first and second materials may be particulate and held in closedspaces against respective sides of the porous member.

Alternatively the first and second materials may be applied as a coatingto the respective sides of the porous member. The coating may be appliedto the porous member by rolling or pointing.

The electrolyte may be sulphuric acid and the first and second materialsrespectively lead oxide and lead.

The invention also provides an accumulator comprising a plurality ofconnected cells adjacent each other of the type described in any of thepreceding ten paragraphs. The cells preferably have respective alternatecommon first and second materials. The accumulator may be of thelead-acid type.

A protective coating is preferably provided around the cell or cells andthis may be formed by dipping the cell or cells in a liquid rubber orplastics material to provide a durable coating.

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic cross-sectional side view through a cellaccording to the present invention;

FIG. 2 is a similar view of an accumulator comprising a plurality offurther cells according to the present invention; and

FIG. 3 is a respective view of part of the accumulator of FIG. 2.

FIG. 1 shows a cell 10 suitable for use in combination with other suchcells in for example a battery for a motor vehicle. The cell 10comprises a plate 12 of porous ceramic material. The ceramic material ofthe plate 12 is porous and the plate 12 has been previously soaked insulphuric acid such that a substantial volume of the pores containssulphuric acid.

The plate 12 is mounted centrally within a rectangular casing 14 whichmay be made for example of a plastics material. The casing 14 isarranged such that spaces are provided on either side of the plate 12.One of these spaces is filled with powdered lead oxide 16 and the otherwith lead powder 18. Strips of lead 20,22 extend from adjacent the baseof the casing through respectively the lead oxide 16 and the lead powder18 and through an upper removable cap 24 of the casing 14 to provideterminals 26,28.

In use, the lead oxide 16 constitutes the anode and the lead powder 18constitutes the cathode and respective connections thereto are providedby the terminals 26,28. Six such cells would be connected together toform a conventional twelve volt battery.

In test after charging for a number of hours the above described cellhas produced a voltage of at least two volts, yet this cell has a weightin the order of half that of a conventional cell comprising lead platesin an acid bath. This cell is considerably safer than a conventionalcell in that a spillage of acid will not occur therefrom even in theevent of the cell being damaged. The construction of this cell is likelyto be more durable than conventional cell. The cell may be readily andthus inexpensively manufactured.

The rigidity of the cell is provided by the ceramic plate and not theactive material (lead/lead oxide) and thus no excess active material isrequired in the cell resulting in the reduced weight. A common cause offailure of conventional lead acid accumulators is flaking or shreddingof the active plates which will not occur with cells according to theinvention.

FIGS. 2 and 3 show a three cell accumulator 30. The accumulator 30 has asandwich configuration with layers (from left to right in FIG. 2) oflead oxide 32, a first ceramic plate 34 which has been soaked insulphuric acid, a layer of lead 36, a second ceramic plate 38, a furtherlayer of lead oxide 40, a third ceramic plate 42, and a further layer oflead 44. The layers of lead oxide and lead 32, 40, 36, 44 are formed onthe ceramic plates 34, 38, 42 by rolling. The lead or lead oxide ismixed with a medium, which may be a rubber compound to form a flexiblemixture which is rolled onto a ceramic plate. The coated plate is thensintered to burn off the organic material. The above described sandwichconfiguration may be sintered as a whole. Alternatively the medium maybe such that the organic material will evaporate away of it volition.

A network 46 (FIG. 3) of a conducting material such as gold is printedon the left hand side of the ceramic plates 34 and 38 and both sides ofthe ceramic plate 44. The networks 46 are provided to ensure electricalconnectivity between the active materials and the electrolyte in theplates 34, 38, 42. Connected to each of the networks 46 is a strip 48 ofa further conducting material which extends upwardly to provideterminals. The strips 48 on the plate 38 and the left hand side of theplate 42 each provide a common terminal for two cells with the otherstrips 48 providing a terminal for just one cell. The sandwichconfiguration is enclosed within a plastic casing 50 with the strips 48extending therethrough. The casing 50 is formed by dipping theconfiguration in a bath of a liquid plastics material.

Various other modifications may be made without departing from the scopeof the invention. For example the lead and lead oxide may be coated onthe ceramic plate by for example painting. A rubber protective coatingcould be provided by dipping. Many different materials other thanceramic could be used for the plate. The requirement for the platematerial being that it is sufficiently porous and inert to theelectrolyte. The apparatus may obviously be used for cells other thanlead-acid cells. The use of a porous member soaked with electrolytecould also be used in primary cells and also in electroplating. Theplate may be differently shaped and its exterior may be contouredthereby providing a greater surface area for contact between the porousmember and the materials either side thereof.

I claim:
 1. An electric cell comprising a self supporting porous memberin which a liquid electrolyte is absorbed; a first material comprisingan anode in contact with the member; a second material comprising acathode in contact with the member; and electrical conductors positionedon the porous member and extending through the cell in contactrespectively with either the first or second materials.
 2. An electriccell according to claim 1, wherein the porous member is substantiallyrigid.
 3. An electric cell according to claims 1 or 2, wherein the firstand second materials are respectively in contact with opposite sides ofthe member.
 4. An electric cell according to claim 3, wherein the firstand second materials are particulate and held in closed spaces againstrespective sides of the porous member.
 5. An electric cell according toclaim 3, wherein the first and second materials are applied as a coatingto the respective sides of the porous member.
 6. An electric cellaccording to claim 5, wherein the first and second materials are in theform of a rolled coating.
 7. An electric cell according to claim 5,wherein the first and second materials are in the form of a paintedcoating.
 8. An electrical cell according to claim 1, wherein theelectrolyte is sulfuric acid and the first and second materialsrespectively are lead oxide and lead.
 9. An electric cell according toclaim 1, wherein the porous member is made of a ceramic material.
 10. Anelectric cell according to claim 1, wherein the porous member has asubstantially planar configuration.
 11. An electric cell according toclaim 1, wherein the porous member has a contoured exteruir,
 12. Anelectric cell according to claim 1, wherein the conductors are printedon the porous member.
 13. An electric cell according to claim 2, whereinthe printed conductors comprise gold.
 14. An electric cell according toclaim 1, wherein additional electrical conductors extend from theconductors in contact with the first and second materials, externally ofthe cell to provide terminals for the cell.
 15. An accumulatorcomprising a plurality of connected electric cells according to claim 1positioned adjacent to each other.
 16. An accumulator according to claim15, wherein the cells have respective alternate common first and secondmaterials.
 17. An accumulator according to claim 16, wherein that theaccumulator is of the lead-acid type.
 18. An accumulator according toclaim 15, wherein a protective coating is provided around the electriccell.
 19. A method of coating electric cells in an accumulator,comprising the step of dipping the cell in a liquid rubber or plasticsmaterial.